Guangzhao Ran

Multilayered graphene used as anode of organic light emitting devices

In this report, we find multilayered graphene, which has good transparency, conductivity and suitable work function, can be used as the anode for the organic light emitting device. Our device structure is Al/glass/multilayered graphene/V2O5/NPB/CBP:(ppy)2Ir(acac)/Bphen/Bphen:Cs2CO3/Sm/Au. The maximum luminance efficiency and maximum power efficiency reach 0.75 cd/A and 0.38 lm/W, respectively. We believe that by optimizing the hole density and uniforming the thickness of the multilayered graphene anode, the device efficiency can be remarkably increased in the future.

Electrical properties of Cu doped p-ZnTe nanowires

Single crystalline zincblende p-ZnTe nanowires (NWs) were synthesized via the vapour phase transport method. Based on either as-grown or Cu doped ZnTe NWs, single NW field effect transistors were fabricated and they were used to study the electrical properties of ZnTe NWs. Electrical transport measurements show that the as-grown ZnTe NWs are of p-type and very high resistivity. After 30 min immersion in Cu(NO3)2 solution, their conductivity can be increased by about three orders of magnitude. The hole concentrations of the p-type ZnTe nanowires could be controlled in a range from 7.0 × 1017 to 3.5 × 1018 cm−3 by changing the immersion duration. The doped p-type ZnTe NWs may have potential applications in nanoscale electronic and optoelectronic devices.

A Selective-Area Metal Bonding InGaAsP–Si Laser

A 1.55-μ m hybrid InGaAsP-Si laser was fabricated by the selective-area metal bonding method. Two Si blocking stripes, each with an excess-metals accommodated space, were used to separate the optical coupling area and the metal bonding areas. In such a structure, the air gap between the InGaAsP structure and Si waveguide has been reduced to be negligible. The laser operates with a threshold current density of 1.7 kA/cm2 and a slope efficiency of 0.05 W/A under pulsed-wave operation. Room-temperature continuous lasing with a maximum output power of 0.45 mW is realized.

Electrical transport and electroluminescence properties of n-ZnO single nanowires

The n-ZnO single nanowire/p+-Si heterojunctions are fabricated using two types (A and B) of ZnO nanowires. Both types of nanowires are synthesized using the vapour phase transport method. Nanowires A, with growth direction along the high index, are grown on Si substrates. Nanowires B, with growth direction along [0001], are grown on In0.2Ga0.8N substrates. The electrical transport properties of nanowires A and B are investigated by fabricating single nanowire field effect transistors. The measured resistivities are 0.06 and 0.001xa0Ωxa0cm, respectively. Sharp UV emission resulting from free exciton recombination in ZnO nanowire is observed in the electroluminescence spectra from both types of n-ZnO single nanowire/p+-Si heterojunctions.

Ultrasensitive Near-Infrared Photodetectors Based on a Graphene–MoTe2–Graphene Vertical van der Waals Heterostructure

Graphene and other layered materials, such as transition metal dichalcogenides, have rapidly established themselves as exceptional building blocks for optoelectronic applications because of their unique properties and atomically thin nature. The ability to stack them into van der Waals (vdWs) heterostructures with new functionality has opened a new platform for fundamental research and device applications. Nevertheless, near-infrared (NIR) photodetectors based on layered semiconductors are rarely realized. In this work, we fabricate a graphene-MoTe2-graphene vertical vdWs heterostructure on a SiO2/p+-Si substrate by a facile and reliable site-controllable transfer method and apply it for photodetection from the visible to NIR wavelength range. Compared to the layered semiconductor photodetectors reported thus far, the graphene-MoTe2-graphene photodetector has a superior performance, including high photoresponsivity (∼110 mA W-1 at 1064 nm and 205 mA W-1 at 473 nm), high external quantum efficiency (EQE; ∼12.9% at 1064 nm and ∼53.8% at 473 nm), rapid response and recovery processes (a rise time of 24 μs and a fall time of 46 μs under 1064 nm illumination), and free from an external source-drain power supply. We have employed scanning photocurrent microscopy to investigate the photocurrent generation in this heterostructure under various back-gate voltages and found that the two Schottky barriers between the graphenes and MoTe2 play an important role in the photocurrent generation. In addition, the vdWs heterostructure has a uniform photoresponsive area. The photoresponsivity and EQE of the photodetector can be modulated by the back-gate (p+-Si) voltage. We compared the responsivities of thin and thick flakes and found that the responsivity had a strong dependence on the thickness. The heterostructure has promising applications in future novel optoelectronic devices, enabling next-generation high-responsivity, high-speed, flexible, and transparent NIR devices.

Efficient silicon quantum dots light emitting diodes with an inverted device structure

We use silicon quantum dots (SiQDs) with an average diameter of 2.6 ± 0.5 nm as the light emitting material and fabricate inverted structure light emitting diodes (SiQD-LEDs) with bottom cathodes. ZnO nanoparticles with high electron mobility, a deep valence band edge, and robust features to resist dissolving by the SiQD solvent were used as the electron transport layer. 1,1-Bis[(di-4-tolylamino)phenyl]cyclohexane (TAPC) with high hole transport mobility and a high lowest unoccupied molecular orbital level was used as the hole transport layer. Poly(ethylene imine) (PEI) modified indium-tin oxide (ITO) was used as the low work function (∼3.1 eV) cathode and MoO3/Al as the high work function anode. Electroluminescence of the SiQD-LEDs is mainly from the SiQDs with a peak located at ∼700 nm. The maximum external quantum efficiencies of the SiQD-LEDs are 2.7%.

Effect of excess PbBr2 on photoluminescence spectra of CH3NH3PbBr3 perovskite particles at room temperature

The organic-inorganic halide perovskites have promising applications in light-emitting devices besides solar cells. We here prepare CH3NH3PbBr3 perovskite particles on SiO2 substrates and find that the photoluminescence (PL) spectrum of the particles at room temperature has two peaks, locating at 529 and 549u2009nm, respectively, much different from that of the corresponding films prepared on the oxygen plasma-cleaned SiO2 substrates, which has a single peak. The double peaks have different temperature-dependence behaviors. By the x-ray diffraction and energy dispersive x-ray spectroscopy analyses, excess PbBr2 is detected inside the particles. We deduce that such excess PbBr2 has introduced shallow level defects. It is concluded that band-to-band recombination and these defects result in the double-peaked feature of the PL spectra of CH3NH3PbBr3 particles at room temperature.

Bonding InGaAsP/ITO/Si Hybrid Laser With ITO as Cathode and Light-Coupling Material

A 1.5-μ.m InGaAsP/ITO/Si hybrid laser with indium tin oxide (ITO) as both a cathode and a light-coupling material is presented. The InGaAsP gain structure with a transparent ITO cathode is flip-chip bonded onto a patterned silicon-on-insulator wafer. The light generated in the InGaAsP multiquantum wells is coupled through the ITO cathode into the Si waveguide to form an InGaAsP/ITO/Si hybrid laser. The threshold current density of this hybrid laser is 20 kA/cm2 at 210 K. Due to the advantages of post-bonding and simplicity of the fabrication process, such a hybrid laser may be a promising Si light source.

Hybrid InGaAsP-Si Evanescent Laser by Selective-Area Metal-Bonding Method

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4-lambda InGaAsP-Si distributed feedback evanescent lasers with varying silicon waveguide width

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